JP2638273B2 - Unique word detection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a unique word detecting device, and more particularly to a device for detecting a unique word contained in a burst in a satellite communication system.

[Conventional technology]

FIG. 5 is a diagram showing a general burst frame configuration, and FIG. 6 is a diagram showing a configuration of a conventional unique word detection circuit.

In FIG. 5, a burst has a carrier reproducing unit 100 composed of an unmodulated carrier, a bit timing reproducing unit 200 composed of a carrier modulated by a clock pulse, and a unique word unit 300 composed of a carrier modulated by a unique word. The data section 400 includes a carrier modulated by a data signal.

In FIG. 6, the PSK modulated wave signal supplied from the input terminal 1 is demodulated by the demodulation circuit 10. The demodulated signal is output from output terminal 2 as received data. The demodulated signal is also detected by a first low-pass filter circuit 11, a squaring circuit 12, a second low-pass filter circuit 13, and a comparison circuit 14 to detect the carrier recovery section at the head of the burst. An aperture generation circuit based on this detection timing (carrier recovery unit start detection signal)
The detection timing of the unique word following the bit timing reproduction unit is estimated from the burst frame configuration predetermined in 16 and an aperture is provided. The aperture generation circuit includes, for example, a delay circuit for delaying the carrier wave recovery section start detection signal, and a one-shot monostable multivibrator triggered by the rise of the output of the delay circuit. The unique word detector 17 detects a unique word from the signal demodulated in the aperture created by the aperture generating circuit 28, and outputs a unique word detection signal from the output terminal 22. In addition, unique
For the structure of the word detector, see, for example, “El
ements of Digital Satellite Communication "Vol.1 (C
OMPUTER SCFENCE PRESS, 1984), p. 342 et seq.

The above operation will be described more specifically. The first low-pass filter circuit 11, the squaring circuit 12, and the second low-pass filter circuit 13 form a DC component extracting means 19. The output of the demodulation circuit 10 is supplied to a first low-pass filtering circuit 11. When carrier synchronization is established in the demodulation circuit 10, the demodulation circuit 10 outputs a DC vector when the carrier recovery unit shown in FIG. 1 is input. The magnitude of this DC vector is determined by a squaring circuit (or absolute value circuit) 12. The output of the squaring circuit is supplied to a second low-pass filtering circuit 13 in order to suppress an increase in signal dispersion due to the squaring circuit. The output level of the second low-pass filter circuit is compared with a preset threshold (TH) in a comparator circuit 14 to detect the start time of the carrier recovery unit.

FIGS. 7A, 7B and 7C show demodulators when there is no signal, when receiving an unmodulated carrier (carrier recovery unit), and when receiving a modulated carrier (bit timing recovery unit or data unit), respectively.
The ten outputs are shown on the phase plane.

As shown in FIG. 7A, the demodulator output when there is no signal is dispersed at the center of its origin when viewed on the phase plane. Even when this is passed through the first low-pass filter 11, the DC component is not detected and is dispersed at the center. The variance after passing through the first low-pass filter 11 is reduced by compressing noise. This magnitude is dispersed around a small value close to zero, and when the magnitude is detected by the squaring circuit 12, it passes through the second low-pass filter 13 to become a value close to zero.

In the case of an unmodulated carrier, the demodulated signal disperses approximately oval as shown in FIG. 7B. This variance is the Phas in demodulator 10.
This is caused by output fluctuation of e lock loof. This signal is
When the light passes through the low-pass filter 11, the dispersion of the oval shape becomes small. When the magnitude of this vector is determined by the squaring circuit 12, a stable non-zero DC value is observed, unlike when there is no signal. From the output of the next low-pass filter 13, a value equal to or higher than a certain level can be obtained, and an unmodulated carrier, that is, a carrier recovery unit can be identified.

When a modulated wave is input, as shown in FIG. 7C, the signal is dispersed by the PLL into an elliptical shape whose center is symmetrical on the phase plane, and the phase in the opposite direction is changed according to the "0" and "1" signals. Output the vector having The vector outputs cancel each other out in the low-pass filter, leaving only the noise component. Therefore, a square circuit
Even if the magnitude is obtained in step 12, the output is similar to that when there is no signal, and the output becomes a value close to zero for the modulated wave. In this way, a stable high-level signal is output to the second low-pass filter 13 at the time of receiving the carrier reproducing section (unmodulated carrier) at the head of the burst.

Therefore, the threshold (T
H), and outputs a reference signal for detecting the timing at which the output signal of the second low-pass filter circuit 13 exceeds the threshold set by the comparison circuit 14 and forming an aperture signal for detecting a unique word. I have.

[Problems to be solved by the invention]

The above-described conventional unique word detection method detects the start time of the carrier recovery unit at the beginning of the burst, and uses the predetermined time as a reference for the carrier recovery unit as shown in FIG. The position where a unique word is to be detected is estimated from the temporal relationship of the word portion, and an aperture signal is generated.

By the way, as shown in FIG. 8, the DC value extracted from the output of the demodulator 10 by the DC component extracting means 19 has a slow rise and a rise time also fluctuates.
This is because the carrier phase synchronization in the demodulator 10 has not been sufficiently established at the time when the leading part of the carrier recovery unit in FIG. 5 is input to the demodulator. The time required for establishing this synchronization also changes depending on the carrier-to-noise ratio (C / N ratio) of the input burst. Therefore, in the technique shown in FIG. 6, the variation in the timing at which the output of the DC component extraction means exceeds the threshold becomes large, and the aperture must be widened in view of this variation. For this reason, it has been difficult to prevent erroneous detection of a unique word.

Accordingly, an object of the present invention is to provide a unique word detection device that can reduce the probability of the above-described unique word erroneous detection.

[Means for solving the problem]

The present invention is a unique word detection device that detects a unique word from a demodulated signal obtained by demodulating a burst signal including a carrier recovery unit, a bit timing recovery unit, a unique word unit, and a data unit with a demodulator, DC component extraction means for extracting a DC component of the demodulated signal; Carrier recovery section end detection means for detecting the end timing of the carrier recovery section from the output of the DC component extraction means; included in the demodulated signal based on the end timing Means for generating an aperture signal for estimating the position of the unique word to be detected; means for detecting a unique word from the demodulated signal based on the aperture signal.

[Action]

According to the present invention, the falling portion of the DC component extracting means, that is, the end point of the carrier recovery section in the burst is detected. Near the end of the carrier recovery section, the carrier phase synchronization has been established in the demodulator, so the demodulation of the carrier recovery section having a sufficiently large DC component of the demodulator output ends, and the demodulation of the bit timing recovery section ends. Is started, the output value of the DC component extracting means sharply decreases. The point at which the output of the DC component extracting means falls is the C / C of the received burst.
Stable extraction is possible even when the N ratio is low. The present invention
Since the aperture signal is generated based on the output drop time, the time when the unique word is input can be accurately estimated. Therefore, the present invention can prevent the erroneous detection of the unique word by narrowing the aperture width.

〔Example〕

Next, a first embodiment of the present invention will be described with reference to FIG.

First Embodiment A demodulator for demodulating a received burst signal
10, a DC component extraction means 19, a comparison circuit 14 for outputting a carrier reproduction section detection signal indicating that the output of the DC component extraction means has exceeded a threshold, and carrier recovery of a reception burst based on the carrier reproduction section detection signal. Control circuit 15 for outputting a carrier recovery section end detection signal indicating the end time of the portion
An aperture generation circuit 16 for outputting an aperture signal for unique word detection based on the carrier recovery section end detection signal; and a demodulator based on the aperture signal.
And a unique word detector 17 for detecting a unique word from 10 outputs.

In FIG. 1, the configurations and operations of the demodulator 10, the DC component extracting means 19 and the comparison circuit 14 are the same as those of the prior art described with reference to FIG. Comparison circuit 14
The carrier recovery unit detection signal output from the control unit 15 is supplied to the control circuit 15. The carrier recovery section detection signal is at a high level while the output of the DC component extraction means 19 exceeds the threshold. The control circuit 15 determines that the carrier reproducing unit has been detected when the carrier reproducing signal has been kept at the high level for a certain time or more. Then, the control circuit 15 detects a point in time when the carrier recovery unit of the reception burst ends and transits to the bit timing generation unit, and outputs a carrier recovery unit end detection signal indicating the detection timing to the aperture generation circuit 16. The configuration of the control circuit 15 will be described later. The aperture generation circuit 16 outputs to the unique word detection circuit 17 an aperture signal for estimating the time and period during which the unique word arrives, based on the carrier recovery section end signal. The unique word detection circuit 17 detects a unique word from the output of the demodulator 10 during the period specified by the aperture signal, and outputs the unique word detection signal to the terminal 3.
Output to

Next, the configuration and operation of the control circuit 15 will be described with reference to FIGS. FIG. 2 is a block diagram showing the configuration of the control circuit 15, and FIG. 3 is a timing chart for explaining its operation.

In FIG. 2, the control circuit 15 controls the comparison circuit shown in FIG.
The carrier recovery section detection signal supplied from 14 is supplied to the counter 32
And a switch circuit 31 to be applied to an enable terminal or a falling edge detection circuit 34, and when a high level signal is given from the switch circuit 31, the count value is increased by a clock supplied from a clock generator (not shown). Counter 32, a comparator circuit 33 for providing the above-mentioned switch switching signal to the switch 31 when the count value of the counter 32 reaches a predetermined value, a falling edge of the output of the switch circuit 31 is detected, and the aforementioned carrier wave reproduction is performed. It comprises a falling edge detection circuit that outputs a section end detection signal, and a delay circuit 35 that delays the carrier recovery section detection signal and supplies it to the clear terminal of the counter 32.

In FIG. 2, the switch switching signal is a switch circuit.
In addition to the signal 31, the signal is also output to the outside of the control circuit 15. The switch switching signal output to the outside of the control circuit 15 is used in a second embodiment of the present invention described later.

The switch circuit 31 includes two selectors 41 and 42. When the switch control signal supplied from the comparison circuit 33 is at a low level, the selector 41 outputs the carrier reproduction section detection signal supplied from the comparison circuit 14 in FIG. 5, and when the switch control signal is at a high level, Output low level. The selector 42 outputs the carrier-wave reproducing unit detection signal when the switch control signal is at a high level, and otherwise outputs a high level.

Next, the operation of the control circuit 16 will be described with reference to FIG. To the switch circuit 31, the carrier recovery section detection signal shown in FIG. At the time of the rising edge of the carrier recovery section detection signal, the switch switching signal shown in FIG. 3C is at a low level, so that the input of the switch circuit 31 is input to the enable terminal of the counter 32 (FIG. b)). When the output of the switch 36 becomes high level, the counter 32 counts clock pulses supplied from a clock generator (not shown) and outputs the count value to the comparator 33. The comparator 33 goes high when the counted value exceeds a predetermined value. The output of the comparator 33 is the switch switching signal described above. When this signal goes high, the switch circuit 31 supplies the carrier recovery section detection signal to the falling edge detection circuit 34 (FIG. 3 (d)). When the switch is switched, the signal input from the switch circuit 31 to the enable terminal of the counter 32 becomes low level (FIG. 3 (b)). The falling edge detection circuit 34
The falling edge of the supplied signal is extracted to obtain a carrier recovery section end detection signal (FIG. 3 (e)). Further, the carrier recovery unit end detection signal is given a delay amount slightly larger than the period during which the value is at the high level by the delay circuit 35 and is input to the counter 32 as a reset signal (FIG. 3 (f)). . When the counter 32 is supplied with the reset signal,
The contents are reset. When the counter 32 is reset, the output of the comparison circuit 33, that is, the switch control signal becomes low level as shown in FIG. 3 (c). When the switch control signal goes low, the switch 31 again inputs the carrier recovery section detection signal to the enable terminal of the counter 32, and waits to detect a unique word for the next arriving burst.

In the control circuit 15 having the configuration shown in FIG. 2, the delayed carrier recovery section end detection signal is used as the reset signal of the counter 32. However, this reset signal is not necessarily used inside the control circuit. No need to generate. For example, if a signal indicating the end of a burst is generated in the received signal processing circuit provided after the unique word detection device of the present invention, the signal can be used as a reset signal for the counter 32 based on this signal. If the unique word detector 17 of FIG. 1 has a function of also generating a unique word non-detection signal, both the unique word detection signal and the unique word non-detection signal are used. Alternatively, the counter 32 may be reset.

The control circuit 15 having the above-described configuration prepares to detect the end point of the carrier wave recovery unit after the DC component of the carrier wave recovery unit becomes sufficiently large. Thereafter, the control circuit 15 outputs the above-mentioned carrier recovery unit end detection signal by detecting the falling edge of the carrier recovery unit detection signal. The reason for performing such preprocessing before detecting the falling edge of the carrier recovery section detection signal is as follows. For example, in the impulse indicated by X in FIG. 3A, if the impulse noise or the like included in the received burst cannot be completely removed by the DC component extracting means 19, the impulse noise other than the carrier recovery unit in the burst is removed. It occurred in the part. If the control circuit is configured in this way, the value of the counter 32 will not exceed a predetermined value even if the carrier wave recovery section detection signal temporarily goes high, and the switch circuit 31 will not be switched. The falling edge of the impulse is not mistaken for the end of the carrier recovery unit. In the DC component extracting means 19, the DC component from the demodulator 10 is sufficiently smoothed by, for example, sufficiently narrowing the pass band of the first and second low-pass filters 11 and 13, and such an impulse If the DC component extraction means is provided with a function for removing such impulse, or if such a function is provided for the DC component extraction means, this control circuit can be configured only with the falling edge detection circuit 34. You can also.

Next, a second embodiment of the present invention will be described. In the first embodiment, the detection of the start time and the end time of the carrier recovery unit are performed using one threshold (TH). In the second embodiment, TH1, TH2 (TH1> TH2)
Are used. More specifically, the arrival of the carrier recovery unit is detected using the threshold TH1, and the end point of the carrier recovery unit is detected using the threshold TH2. The advantages provided by using these two thresholds will be described later.

FIG. 4 is a block diagram showing a second embodiment of the present invention. In FIG. 4, the only difference from FIG. 1 is the portion relating to the comparison circuit 14, the control circuit 15, and the selector 20. Hereinafter, the description will be limited to this part.

In FIG. 4, the DC component of the output of the demodulator 10 output from the DC component extracting means 19 is given to one input of a comparison circuit 14. The selector 20 responds to the switch control signal supplied from the control circuit 15 by two thresholds TH1,
One of TH2 is supplied to the other input of the comparison circuit 14. In addition,
This switch control signal has already been described with reference to FIG. The selector 20 has a large threshold (TH1) during the period of detecting the input of the carrier recovery unit, that is, when the switch control signal is at a low level.
During the period in which the end point of the carrier recovery unit is to be detected, that is, when the switch control signal is at a high level, the smaller threshold (TH2) is output. Comparison circuit 14
Is a signal indicating whether or not the output of the DC component extraction means 19 exceeds the given threshold based on the threshold thus given, that is,
The carrier wave reproducing section detection signal is output to the control circuit 15. The configuration and operation of the control circuit 15 are as follows.
The control circuit 15 is the same as the control circuit 15 described with reference to FIG. The control circuit 15 generates a carrier reproduction section end signal and supplies the signal to the aperture generation circuit. The operations of the aperture generating circuit 16 and the unique word detector 17 are the same as those of the prior art described with reference to the first embodiment and FIG. 6, and a unique word detection signal is output to the terminal 3. Here, advantages of the second embodiment over the first embodiment will be described.

In the first embodiment, the start time and the end time of the carrier recovery unit are detected using one threshold (TH). In this case, the problem is how to determine TH. If TH is set to a small value, the probability of erroneously recognizing that the carrier recovery unit has arrived in a portion other than the carrier recovery unit due to noise or the like increases. That is, erroneous detection of the start time of the carrier recovery unit occurs.

This erroneous detection is likely to occur when the C / N ratio of the received burst is low.

If TH is increased, erroneous detection of the carrier wave reproducing section start time does not occur. However, when the C / N ratio of the received burst is low, the output of the DC component extracting means 19 in the carrier recovery unit is likely to fluctuate. Therefore, there is a possibility that a change in the output of the DC component extraction unit may be erroneously recognized as the end of the carrier recovery unit.

In the second embodiment, such a problem does not occur because the start time of the carrier recovery unit is determined by the threshold of a large value and the end time of the carrier recovery unit is determined by the threshold of a small value.

〔The invention's effect〕

As described above, when detecting a unique word, the present invention determines that burst reception is performed by detecting the start time of the carrier recovery unit, and then terminates the carrier recovery unit with low detection timing variance even at low C / N. The time is being detected. Then, based on the detection time, the timing at which the unique word is detected is estimated, thereby accurately estimating the position where the unique word is detected, with high probability (without missing or erroneously detecting). Unique words can be detected. In particular, in a burst transmission system such as a voice activation system in which arrival of a burst cannot be predicted at all and initial phase synchronization tends to be slow, the present invention is particularly effective.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the unique word detection circuit of the present invention, FIG. 2 is a block diagram showing a configuration of a control circuit used in the embodiment of the present invention, and FIG. 4 is a timing chart for explaining the operation of the control circuit. FIG. 4 is a block diagram showing a second embodiment of the unique word detection circuit of the present invention. FIG. FIG. 6 is a block diagram showing the configuration of a unique word detection circuit in the prior art. FIGS. 7A to 7C are diagrams showing the output of the demodulator 10 in FIG. 2 on a phase plane. The figure shows the output waveform of the DC component extracting means 19 in FIG. In the figure, 10: demodulator, 11, 13: low-pass filter circuit, 12: square circuit, 14, 33: comparison circuit, 15: control circuit, 16: aperture generation circuit, 17: Unique word detector, 31…
... Switch circuit, 32 counter, 34 falling edge detection circuit, 35 delay circuit, 41, 42 selector.

Claims (4)

(57) [Claims] 1. A unique word detection system for detecting a unique word from a demodulated signal obtained by demodulating a burst signal including a carrier recovery section, a bit timing recovery section, a unique word section, and a data section by a demodulator. A DC component extraction unit for extracting a DC component of the demodulated signal; a carrier recovery unit end detection unit for outputting a carrier recovery unit end detection signal indicating an end timing of the carrier recovery unit from an output of the DC component extraction unit; Means for generating an aperture signal for estimating the position of a unique word included in the demodulated signal based on the demodulated signal; means for detecting a unique word from the demodulated signal based on the aperture signal; method. 2. The unique word detection method according to claim 1, wherein said carrier recovery unit end detection means compares said DC component with a threshold value, and said output of said comparison means maintains one level at a certain time. Same level continuation determining means for determining that the output of the comparing means has transitioned from the one level to the other level after the one level has continued for a predetermined time, and the carrier recovery section end detection signal And a level transition detecting unit for outputting a unique word. 3. The unique word detection system according to claim 2, wherein said carrier recovery section end detection means sets a threshold value of a large value when said comparison means is at said one level, and sets a threshold value of said large value when said comparison means is at said other level. Is a unique word detection method further provided with a threshold output means for outputting a small threshold value. 4. The unique word detection method according to claim 1, wherein said carrier recovery section end detection means compares said DC component with a threshold value, and said comparison means outputs said carrier signal from said carrier recovery section. And a means for detecting a change point indicating a transition to a bit timing reproducing unit.